1. Field of the Invention
The retainer system of the invention relates to electrical heater devices that employ positive temperature coefficient resistors (“PTC resistors”) and the means and methods of securing PTC resistors within such heater devices.
2. Description of the Related Art
PTC resistors are well known in the art and are frequently used in small electrical heater devices. Examples of such electrical heater devices are small heaters designed to dispense volatiles into the air. Such volatiles include scents, insect control active ingredients, and the like. For example, WO 2006/046209 discloses a form of positive temperature coefficient electric heating device for vaporizing insecticides and fragrances impregnated in a solid mat. A variety of heating elements have been developed for these and analogous applications. See generally U.S. Pat. Nos. 4,037,082, 4,251,714, 4,635,026, 4,728,779, 4,814,584, 5,262,619, 6,192,169, 6,374,045, 7,012,222; and PCT international publications WO 97/02054, WO 97/45008, and WO 98/57674; and European patent application EP 0 965 267.
PTC resistors, such as that used in the device of WO 2006/046209, typically have a generally flat, pill-like shape having a selected thickness. The PTC resistor must be firmly secured between two electrical contacts, thus completing a circuit that allows electrical current to flow through the PTC resistor, causing it to heat. A failure to secure the PTC resistor can lead to unreliable electrical contacts and therefore unreliable heating. Also, if the PTC resistor is held within a space larger than the resistor, the same means that secure it to ensure good electrical contact may also function to prevent the resistor's movement should the device within which it is located be shaken, dropped, or the like. PTC resistors are fairly delicate and subject to breakage.
Also, in many devices, the electrical terminal/contact retainer system which has a pressure contact with the PTC resistor is a stamped part. As a result, there will occasionally be sharp edges, such as stamping burrs, formed on the electric contact. When these sharp edges come into contact with the fragile PTC resistor, there can be an incidence of cracking of the PTC resistor over time, particularly as it heats and cools through use.
Therefore, the art is continually challenged to create ways to secure PTC resistors by retainer systems and assembly techniques that successfully firmly hold the resistors, with good electrical contact, but with carefully controlled pressures and without sharp edges that could initiate cracking of the PTC resistor. Accordingly, the present invention is directed to meeting these needs.